6 BRITISH LICHENS : 
: 37. Usnea Dill. Thallus filamentose, internally with chondroid 
axis: apothecia terminal or lateral, the margin often ramuloso- 
ciliate, concolorous, with simple spores ; spermogones with simplish 
sterigmata and straight spermatia. ‘ 
Tribe XI. ALECTORIEI Nyl. Thallus much branched, rounded 
or compressed, with woolly medulla: apothecia parmelioid, scutelli- 
form. 
38. Alectoria Ach. Thallus usually filamentose and intricately 
branched; medulla arachnoid or lacunose: apothecia terminal or 
pseudo-terminal, discolorous, with simple or very rarely murali- 
divided spores; spermogones with pauci-articulate sterigmata and 
acicular straight spermatia. 
Tribe XII. CETRARIEI Nyl. Thallus fruticulose or foliaceous, 
with white woolly medulla: apothecia parmelioid, marginal, obliquely 
affixed, 
39. Cetraria Ach. Thallus fruticulose, laciniose, rarely fistulose : 
apothecia subconcolorous, with simple spores; spermogones with 
simple sterigmata and cylindrical spermatia. 
40. Platysma Nyl. Thallus fruticulose or membranaceo-lobed : 
apothecia discolorous, with simple spores ; spermogones with simplish 
or pauci-articulate sterigmata, and various (not cylindrical) sper- 
matia. 
Series IV. PHYLLODEI Nyl.  Thallus foliaceous, usually 
depressed, lobate: apothecia generally parmelioid or lecanorine, 
discolorous. ’ 3 
Tribe XIII. PARMELIEI Nyl. Thallus frondosely dilated, or 
lobate, or laciniate, with woolly, rarely solid medulla: apothecia 
parmeleine rarely lecanorine. 
41. Evernia Ach. Thallus laciniose or much branched, flaccid ; 
medulla arachnoid or partly chondroid: apothecia lateral with simple 
Spores; spermogones with pauci-articulate sterigmata and acicular 
straight spermatia. 
42. Parmelia Ach. Thallus variously lobed or laciniate, usually 
fibrilloso-rhizinose, rarely glabrous bencath; medulla woolly, lax: 
apothecia superficial, with simple spores ; spermogones with pauci- 
articulate sterigmata and .acicular apically fusiformi-incrassate 
spermatia. 
43. Parmeliopsis Nyl. Thallus stellato-laciniate, sparingly rhizi- 
nose beneath ; medulla woolly, lax: apothecia superficial, with simple 
spores ; Spermogones with simple sterigmata and cylindrical arcuate 
.spermatia. 
